Coffee beans produce colors, taste and smell by roasting. Coffee beans are usually accommodated in a roasting space of a roasting container, and the coffee beans accommodated in the roasting space are roasted with hot air supplied by a hot air supplying means. Exhaust gas generated in the roasting space in the roasting container by roasting the coffee beans is usually discharged by an exhaust gas discharging means. As factors for determining the roasting state of the coffee beans, there can be listed temperature of the roasting space, time for roasting, and the amount of exhaust gas.
More specifically, the color of the coffee beans is gradually changed to a thick color of dark brown from green of raw beans via light brown in accordance with the progress of the roasting process. At that time, the color of the coffee beans becomes darker if the temperature becomes is higher and the time is longer. Likewise the color is lighter if the temperature is lower and the time is shorter. The temperature of this hot air can be adjusted by, for example, a burner, as the hot air supplying means. Also, the color of the coffee beans becomes darker if the amount of exhaust gas is smaller because the coffee beans are smoked. Likewise the color of the coffee beans is lighter if the amount of exhaust gas is larger because they are not smoked. The amount of exhaust gas is adjusted by, for example, an exhaust gas damper as the exhaust gas discharging means.
Devices for controlling the temperature during the time that coffee beans are being roasted, are disclosed in Japanese Patent Publication No. Sho 56-19986 and Japanese Utility Model No. Sho 58-2239 and Japanese Utility Model Publication No. Sho 58-33920. Also, devices for controlling the time, are those disclosed in Japanese Utility Model Publication Nos. Sho 59-41989 and 63-1838. Furthermore, a device for controlling the amount of exhaust gas, is disclosed in Japanese Patent Publication No. Sho 61-31981.
Although the above-mentioned temperature and time are important to the roasting state of the coffee beans, the adjustment of the amount of exhaust gas is also important to it. In other words, if the exhaust damper disposed at the exhaust passage is closed to decrease the amount of exhaust gas, the coffee beans become dark in color because they are smoked, and if the exhaust damper is opened to increase the amount of exhaust gas, they become light in color because they are not smoked. Accordingly, in order to roast the coffee beans to a desired color, the adjustment of the amount of exhaust gas is important.
Also, when the roasting process of the coffee beans has progressed, the central portions of the coffee beans are dilated and the so-called silver skin is discharged. This silver skin is discharged into the exhaust passage from the roasting space by the exhaust gas stream and separated from the exhaust gas by a cyclone as a dust removing device disposed on a downstream side of the exhaust passage.
However, if the amount of exhaust gas is large and the velocity of the exhaust gas stream is fast, the silver skin is not dropped within the cyclone, but instead flows into the after-cyclone stage. In the case just mentioned, if an afterburner is attached to the after-cyclone stage, there is fear that the silver skin may ignite and combust into fire. On the other hand, if the amount of exhaust gas is small and the velocity of the exhaust gas stream is slow, the silver skin cannot be discharged from the roasting space and the taste is deteriorated owing to coexistence of the silver skin with the coffee beans.
In order to roast the coffee beans into desired color and in order to make it possible to discharge the silver skin, the amount of exhaust gas must be adjusted properly.
However, the amount of exhaust gas is changed not only by such factors as temperature of the combustion space, etc. but also by such things as the seasons, weather and the like. If a dust arrester, a deodorizing device or the like is connected to the downstream side of the exhaust passage in order to prevent dust and odor of silver skin, etc. generated by the roasting coffee beans from being discharged, back pressure, which is irregularly changeable, is generated to the exhaust passage by this device. As a result, the amount of exhaust gas is fluctuated by this back pressure irrespective of the fact that the opening- and closing state of the exhaust damper is constant.
Because of the foregoing inconveniences, it was difficult for non-technicians to finely regulate the amount of exhaust gas in order to reproduce a particular roasting state of the coffee beans. A high-degree of knowledge and experience was required for roasting the coffee beans, and it was not an easy job to roast the coffee beans into a particular roasting state.
Through extensive study and experiment, the inventor of this application has found that the pressure value of the roasting space of a roasting container for containing the coffee beans exerts influence on the roasting state of the coffee beans.
This means that the same roasting state can be reproduced by detecting and recording a pressure value of a roasting space as a method for numerically catching the change of the roasting state of the coffee beans caused by such factors as temperature of the roasting space, the amount of exhaust gas, seasons and weather, and regulating the pressure value of subsequent roastings space in the roasting such that the pressure value becomes a recorded pressure value as mentioned above. In other words, by recording a pressure value of a particular roasting state of the coffee beans and regulating the pressure value of the roasting space, the pressure value is adjusted to the recorded pressure value mentioned above. Therefore, a particular roasting state (or identical roasting state) can be produced without a high-degree of knowledge and experience.
Until now, the amount of exhaust gas was adjusted by detecting only the temperature of the hot air and the amount of exhaust gas. Because of this, a fine adjustment of the pressure value of the roasting space was difficult to attain merely by adjusting only the temperature of hot air and the flow rate of exhaust gas, as in the prior art and therefore, the coffee beans were difficult to easily roast into a particular roasting state.
It is therefore an object of the present invention to realize a coffee bean roasting device capable of finely adjusting a pressure value of a roasting space, thereby easily reproducing a particular roasting state of coffee beans without a high-degree of knowledge and experience.